Contraction A ‘1 of a flow rate when entering into a cross-section constriction. It arises when the wall of cross-section A 1 is removed (Figure S 98).
The jet contraction becomes smaller as the transition from A 3 to A 1 becomes more round. The contraction coefficient ψ is between 0.6 for sharp edges, 0.7 to 0.8 in the case of a slight rounding, and up to 0.99 in the case of large radii.
Figure S 98: Jet contraction